Journey of disabling filename expansion for Bash alias¶
I wanted to disable Bash pathname expansion for my Bash alias:
alias g='git'
As expected I found solution from Stackoverflow, so I modified my alias to be:
function consume_noglob() {
local command="$1"
shift
$command "$@"
set +o noglob
}
alias g='set -o noglob; consume_noglob git'
However this solution fails to work with pipes. For example:
$ echo "commit message" | g commit -F -
will be equivalent to:
$ echo "commit message" | set -o noglob; consume_noglob git
which means, as pipes have higher precedence over list separators,
the commit message will be piped to set
insted of to git inside consume_noglob.
To solve this problem, I had plan to do following:
alias g='<stash_pipe_cmd>; set -o noglob; <pop_pipe_stash_cmd> | consume_noglob git'
where <stash_pipe_cmd> would store the piped data sowhere and then <pop_pope_stash_cmd> could pipe it to git.
Note
In the follwing discussion enviroment variable __pipestashdir contains path to directory which can be used as runtime directory [1].
In my first impelemntation of <stash_pipe_cmd> and <pop_pipe_stash_cmd>,
I naively thought that I could just use cat and Bash redirections:
# <stash_pipe_cmd>
function pstash() {
# Use $1 as the name for the stash.
cat - > "$__pipestashdir/$1"
}
# <pop_pipe_stash_cmd>
function ppstash() {
local stashname="$__pipestashdir/$1"
if ! [[ -f "$stashname" ]]; then
# No stash exits, so do nothing.
return 0
fi
cat "$__pipestashdir/$1"
rm "$stashname"
}
With this solution
$ echo "commit message" | g commit -F -
seems to work, but if the alias is used on its own it will hang:
$ g --version
as cat will read until EOF and stdin is connected to terminal.
In pstash this can be checked and only use cat if it is not:
function pstash() {
local stashname="$__pipestashdir/$1"
rm -f "$stashname" # Override current potential unused stash
if [[ -t 0 ]]; then
# stdin is connected to terminal,
# so there is nothing to read.
return 0
else
cat - > "$stashname"
fi
}
Now alias:
alias g='pstash galias; set -o noglob; ppstash galias | consume_noglob git'
will be usable in pipes and everything is good…, only there is one problem, git’s interactive adding:
$ g add -i
will exit immediatly. This is because, apparently interactive adding reads standard input for commands and exits if EOF is given, so in:
alias g='pstash galias; set -o noglob; ppstash galias | consume_noglob git'
ppstash galias | consume_noglob git will always make interactive adding exit immediatly.
To fix this, one would need to conditionally pipe the stash to git if it exists.
Condition check can be implemented as simple function:
# Pipe stash Contains
function pstashc() {
[[ -f "$__pipestashdir/$1" ]]
}
but simple inline if statement:
alias g='pstash galias; set -o noglob; if pstashc galias; then ppstash galias | consume_noglob git; else consume_noglob git; fi'
will not work with arguments, e.g.:
$ g --version
so the conditional logic has to be done inside of a function.
As consume_noglob already is a function I modified it to consume the stash too:
function consume_noglob_and_pstash() {
local stash="$1"
local command="$2"
shift 2
if pstashc "$stash"; then
ppstash "$stash" | $command "$@"
else
$command "$@"
fi
set +o noglob
}
so the final alias ended up being:
alias g='pstash galias; set -o noglob; consume_noglob_and_pstash galias git'
this works with in pipes without breaking pipes and g add -i.
Full code can be found at [2].
Footnotes
# Returns 0 if $1 is modifiable directory and 1 otherwise.
function is_modifiable_directory() {
[[ -d "$1" ]] && [[ -w "$1" ]] && [[ -r "$1" ]]
}
# Creates unique runtime directory: `/runtime/dir/$1-XXXXXXXXXX`,
# where `/runtime/dir/` is the first that exists from:
#
# - $XDG_RUNTIME_DIR
# - $TMPDIR
# - /tmp
#
# exits with status 10 if none of these is found.
#
# The path of created temporary directory is wirtten to stdout.
function create_runtime_dir() {
if [[ -z "$1" ]]; then
echo "error: no label given"
echo "usage: create_runtime_dir <label>"
exit 1
fi
local runtime_dir
if is_modifiable_directory "$XDG_RUNTIME_DIR"; then
runtime_dir="$XDG_RUNTIME_DIR"
elif is_modifiable_directory "$TMPDIR"; then
runtime_dir="$TMPDIR"
elif is_modifiable_directory "/tmp"; then
runtime_dir="/tmp"
else
echo "error: no system runtime directory found"
return 10
fi
mktemp -d "$runtime_dir/$1-XXXXXXXXXX"
}
function program_exists() {
if ! command -v "$1" &> /dev/null; then
echo "<the_command> could not be found"
exit 1
fi
}
# Returns 0 if $1 is modifiable directory and 1 otherwise.
function is_modifiable_directory() {
[[ -d "$1" ]] && [[ -w "$1" ]] && [[ -r "$1" ]]
}
# Creates unique runtime directory: `/runtime/dir/$1-XXXXXXXXXX`,
# where `/runtime/dir/` is the first that exists from:
#
# - $XDG_RUNTIME_DIR
# - $TMPDIR
# - /tmp
#
# exits with status 10 if none of these is found.
#
# The path of created temporary directory is wirtten to stdout.
function create_runtime_dir() {
program_exists mktemp || exit 1
if [[ -z "$1" ]]; then
echo "error: no label given"
echo "usage: create_runtime_dir <label>"
exit 1
fi
local runtime_dir
if is_modifiable_directory "$XDG_RUNTIME_DIR"; then
runtime_dir="$XDG_RUNTIME_DIR"
elif is_modifiable_directory "$TMPDIR"; then
runtime_dir="$TMPDIR"
elif is_modifiable_directory "/tmp"; then
runtime_dir="/tmp"
else
echo "error: no system runtime directory found"
return 10
fi
mktemp -d "$runtime_dir/$1-XXXXXXXXXX"
}
__pipestashdir="$(create_runtime_dir pipestash)"
# Pipe stash
function pstash() {
if [[ -z $1 ]]; then
echo "error: missing <stashname>"
echo "usage: pstash <stashname>"
return 1
fi
local stashname="$__pipestashdir/$1"
rm -f "$stashname"
if [[ -t 0 ]]; then
# stdin is connected to terminal,
# so there is nothing to read.
return 0
else
cat - > "$stashname"
fi
}
# Pipe stash Contains
function pstashc() {
[[ -f "$__pipestashdir/$1" ]]
}
# Pop Pipe stash
function ppstash() {
if [[ -z $1 ]]; then
echo "error: missing <stashname>"
echo "usage: ppstash <stashname>"
return 1
fi
local stashname="$__pipestashdir/$1"
if ! [[ -f "$stashname" ]]; then
# No stash exits, so do nothing.
return 0
fi
cat "$stashname"
rm "$stashname"
}
# Pipes pstash $1 to $2 if it exists.
# Disables noglob after the call.
function consume_noglob_and_pstash() {
if [[ -z "$1" ]] && [[ -z "$2" ]]; then
echo "error: <pstash> and <command> missing"
echo "usage: consume_noglob_and_pstash <pstash> <command>"
return 1
fi
local stash="$1"
local command="$2"
shift 2
if pstashc "$stash"; then
ppstash "$stash" | $command "$@"
else
$command "$@"
fi
set +o noglob
}
alias g='pstash g_bash_alias; set -o noglob; consume_noglob_and_pstash g_bash_alias git'